In a bid to reduce population, the dead are allowed to live again virtually, and when it becomes illegal for living people to post their opinion online, billions commit suicide while others risk their lives.

As the previous commenters have said, you have only set up the world. With more consideration for word real estate, this could be phrased as:

"In a world where an online afterlife has made suicide enticing for billions..."

Then, you are missing all 3 elements of the formula: EVENT, CHARACTER, and ACTION.

Re the world, you may want to check the graphic novel Elysium Online by the Greek comic artist Ilias Kyriazis: https://www.goodreads.com/en/book/show/18753600-elysium-online#

This idea has a logic problem,

If people don't die; but become 'undead'

The population of the earth would rise dramatically

As mikepedley said.? I think you have an intriguing premise, but it needs a specific plot, one focused on a singular protagonist.

This isn't really a logline. It's simply setting the stage. We need an individual story within this world to follow - our protagonist's story.

Check out the formula or give the generator a go - links at the top. Both of these are really useful resources when it comes to creating a good logline.

Hope this helps.

UPDATE 2:

The dead are given access to a virtual world that is restricted from the living, who must only observe it. Billions commit suicide to go viral while others risk their lives to expose cyber-inequality.

UPDATE 1:

The dead are allowed to live again virtually and it becomes illegal for living people to post their opinion online. Billions commit suicide to go viral while others risk their lives to expose cyber-inequality.